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Biggest known star discovered

A cluster of massive stars which includes R136a1, or the most massive star ever [AFP]

"To put that into perspective; the nearest star to our sun is only four light years away," Dr Parker, expert on the evolution of star clusters, said.

Scientists say the star, called R136a1, may have been as large as 320 solar masses when it first formed, but has shed some of its initial mass over time.

Dr Parker said the find was "incredibly significant" because it has changed scientists' understanding of how massive it is possible for a star to be.

"Until recently people assumed that there was a fundamental upper limit to how massive a star could be and that upper limit was 150 times the mass of our own sun, which in itself is quite large," he said.

The star was the most massive of several giants identified by the team of scientists.

While other stars can be larger, notably the swollen crimson-coloured ones known as red giants, they are far less heavy.

The mass of the stars in the R136a cluster means they are tens of times bigger than the Earth's sun and brighter and hotter too.